Patents; Updating the Emergency Broadcast System (remember that?) for use on digital television.

By Sabra Chartrand

Published: April 7, 2003

IN these days of heightened states of alert, two inventors have won a patent for a way to make the nation's Emergency Alert System operate more efficiently with modern digital television systems.

The system has been renamed since it broadcast those familiar words: ''This is a test of the Emergency Broadcast System -- this is only a test.'' And while the system's main role used to be to warn of a then-feared Soviet attack, it is no stretch to imagine alerts of a very different nature now.

With fears of terrorism having been elevated by the attacks of September 2001 and developments since, the Department of Homeland Security has created a five-tier color-coded advisory system to warn the public that the menace is low, guarded, elevated, high or severe. The Emergency Alert System (the name was changed in 1994) could play a role if those advisories became more specific -- if, for example, terrorism required evacuation of a specific area.

The two inventors, Timothy Addington and Azita Manson, of Scientific-Atlanta in Lawrenceville, Ga., have won a patent that they say makes it more efficient for digital television systems like DirecTV and EchoStar to carry emergency alerts. Those systems can already do so. But Mr. Addington and Ms. Manson say their invention will make it faster and easier. They also say that their system can be used with a hybrid of analog and digital equipment for television services that have both kinds of equipment as broadcasters make the transition from one to the other.

The Emergency Broadcast System was introduced in 1951 so the president could take over the airwaves in case of an attack or other national emergency, but it has never been used that way. In 1963, the White House began authorizing state and local agencies to use the system for emergencies. Few people, though, have actually heard a real alert, which typically involves a warning of a hurricane, flood or other natural disaster.

Of the more than two dozen codes issued for emergency alerts by the Federal Communications Commission, a majority are for different kinds of severe weather. Only two relate to civil emergencies and evacuation orders. In early 2002, the F.C.C. added an emergency code so that radio and television stations could interrupt programming to broadcast information about child abductions.

All AM, FM and television broadcast stations are part of the Emergency Alert System, and since 1998, all cable systems with 10,000 or more subscribers must take part as well.

When a television station receives notice from the Emergency Alert System, it must integrate the message into the television signal for delivery and display to the subscribers. Viewers might see a message that pre-empts regular programming, or one that is delivered as a ''crawl'' across a TV screen.

In an analog system, Mr. Addington and Ms. Manson say, the message must be overlaid on the desired channels by adding the message to the equipment that controls the channel signal. But in a digital system, that task is multiplied because many more channels are involved, and the equipment that controls the signals typically processes a data stream that includes encoded data for multiple channels, they add.

This would require the modulator to perform the additional tasks of decoding, overlaying and re-encoding the digital data stream, the inventors write.

In addition, there are many different digital subscriber television systems with many different data formats for text and audio data. So any emergency alert must adapt to different formats.

The inventors call their device an interface between digital television systems and emergency alert equipment. It first converts an emergency text message into a display file. If there is an audio message, it is also converted into one of several standard audio files.

The digital alert message may include a display file and an audio file, may indicate that there is no file, or indicate the location of a display or audio file, the inventors say.

The digital message can be stored with the Emergency Alert System, on a server or elsewhere in a digital system depending on convenience, they explain. It allows one alert message to be transmitted as multiple digital messages, and the system can be programmed to repeat the emergency message at set intervals.

For several years, the F.C.C. has used digital technology to distribute alert messages. A digital signal has several advantages. The National Weather Service signal is digital so the weather signals can be decoded and immediately broadcast by television and radio systems. Specially designed television sets, radios, pagers and other personal electronic devices can be programmed to decode the signal and turn themselves on for any emergency alert. Emergency information can be customized for specific areas. And information can be transmitted to television, radio and cable stations and rebroadcast even if no one is working at the facility.

Mr. Addington and Ms. Manson received patent number 6,543,051, which belongs to Scientific-Atlanta.